C6 to C15 alcohols are produced in large volumes throughout the world by the hydroformylation of olefins to produce aldehydes, followed by hydrogenation of the aldehydes to produce alcohols. The olefins that are used as feeds for the hydroformylation are generally oligomers of olefins that are obtained from petroleum feedstocks. Various processes may be used to produce the olefins used for hydroformylation. For example, the octenes that are used in the production of nonyl alcohol, which is produced in large volumes for the manufacture of plasticiser ester, may be produced by the dimerisation of butenes employing a nickel containing catalyst, e.g. by the Octol® or Dimersol® processes, or dimerisation on a zeolite or other acidic catalyst. These are processes which yield substantially pure octenes. Alternatively olefin mixtures averaging about eight carbon atoms may be obtained by the oligomerisation of olefin mixtures using acid catalysts such as phosphoric acid catalysts.
In both these processes, due to the petroleum origins of the olefins, the olefins typically contain impurities such as sulphur and chlorine which can have a damaging effect on the hydroformylation reaction and, in particular, the hydrogenation reactions. The hydrogenation reactions are performed by catalytic hydrogenation at elevated temperature and pressure and the conditions must be carefully controlled in order to optimise the yield and selectivity of the hydrogenation, ensure safe operation of the hydrogenation unit, secure commercially viable catalyst life and minimize side reactions.
Alternative processes for producing alcohols may comprise the hydroformylation of lower carbon number olefins, such as ethylene, propylene and butenes to the corresponding aldehyde or aldehyde mixtures containing one more carbon number than the starting olefin or olefins. These aldehydes, or mixtures thereof, are then subjected to aldolisation to produce condensation products, typically higher aldehydes containing an extra carbon-carbon double bond, often referred to as enals. These enals or enal mixtures may be hydrogenated to the corresponding saturated aldehydes or aldehyde mixtures, or directly to the corresponding alcohols or alcohol mixtures. Examples of products produced by such processes are 2-methylpentanol, 2-ethylhexanol, 2,4-dimethylheptanol and 2-propylheptanol, but other alcohols and alcohol mixtures produced in this way are also known.
A variety of catalysts have been proposed and used in the hydrogenation of aldehydes to produce alcohols and in certain commercial operations a mixture of catalysts have been used in order to optimize the selectivity of the hydrogenation. For example United Kingdom Patent 2142010 employs a two stage hydrogenation process employing a molybdenum disulphide on carbon catalyst in the first stage and a nickel oxide on Kieselguhr catalyst in the second stage. The process is said to hydrogenate an aldehyde feed containing organosulphur impurities which derive from sulphur impurities in the olefin feed.
Australian Patent Application 200197176 A1 relates to the hydrogenation of aldehydes to produce alcohols and discloses that water should be present in the hydrogenation reactor to hydrolyse formic acid esters, acetals, enol ethers, aldol condensation products and other hydrolysable substances. According to Australian Patent Application 200197176 A1 where a series of hydrogenation reactors connected in series are used, the water may be added before the individual reactors and only the amount required may be added at the beginning in order to prevent formation of a second water phase in the hydrogenation reactor.
It is also known from U.S. Pat. No. 5,324,420 that desulphurisation of the olefin feed to hydroformylation can enhance catalyst life in the production of alcohols especially in the hydrogenation stage.
It is also known that the production of formic acid esters during hydroformylation may be reduced if water is present during the hydroformylation reaction as described in “New Syntheses with Carbon Monoxide” by J. Falbe on page 71. Accordingly water may be injected into the hydroformylation reactor and, in this instance, generally an excess of water is used. Water is therefore often present in the product of hydroformylation.
Following hydroformylation and prior to hydrogenation the product of hydroformylation is subject to catalyst removal and water washing which can also result in the presence of water in the material that is fed to hydrogenation.